The present invention relates to an apparatus for applying process solution, such as resist solution, to coat a substrate with a film of the process solution in a process of manufacturing, for example, a semiconductor-device or a LCD.
In the step of performing photolithography to manufacture a semiconductor device, a wafer is coated with resist solution, thereby forming a resist film on the wafer. The resist film is exposed to a predetermined circuit pattern and then developed, thus forming a specific pattern in the resist film.
To coat wafers with resist solution, spin coating is generally utilized. In the spin coating, a wafer is held on a spin chuck by means of vacuum suction. The resist solution is dripped onto the wafer while a motor rotates the wafer. The solution spreads over the entire surface of the wafer by virtue of centrifugal force, forming a resist film having a predetermined thickness. A pump, such as a bellows pump, is used to drip the resist solution onto the wafer. That is, the pump discharges the solution in a prescribed amount and at a predetermined rate.
In recent years, device patterns have become more complex, each consisting of more components arranged in higher density. The thickness uniformity of resist film is therefore considered very important. Since resist solution is expensive, it is necessary to apply the solution to a wafer in an amount as small as is possible. Hence, it is demanded that the resist solution be applied in a small amount and that the resist solution forms a resist film having a uniform thickness.
To meet the demand, the conditions of applying resist solution to a wafer must be minutely controlled in accordance with the physical properties of the resist solution. These conditions cannot be controlled in the conventional apparatus and method for applying resist solution. Particularly in a conventional apparatus, wherein nozzles are interchangeably used, one at a time, to apply various types of resist solutions to wafers, the resist solutions are applied at the same rate though they differ in physical properties. Consequently, it is difficult to form resist film having an appropriate uniform thickness.
The present invention has been made in view of the foregoing. Its general object is to provide an apparatus, which can apply process solution, such as resist solution, forming a resist film of the solution having a uniform thickness even if the solution is applied in an extremely small amount.
A more specific object of this invention is to provide a process solution applying apparatus which can serve to form a film of the solution having a uniform thickness, whichever type of solution it applies.
According to the main aspect of the invention, there is provided a process solution applying apparatus comprising: a substrate holding mechanism holding a substrate; a process solution supplying system for applying process solution in a prescribed amount to the wafer held by the substrate holding mechanism; and a substrate rotating mechanism for rotating the substrate holding mechanism. The process solution supplying system has a supplying mechanism for changing a rate at which the process solution is supplied. When the substrate rotating mechanism rotates the substrate holding mechanism, the wafer is rotated at a predetermined speed to spread the process solution by virtue of centrifugal force and to coat the substrate with the process solution.
Having this structure, the process solution applying apparatus can apply resist solution at a controlled rate, thereby forming a film having a uniform thickness on the entire surface of a wafer, even if the solution is applied to the wafer in a very small amount of 2.0 mL or less which may otherwise greatly influence the thickness uniformity of the film.
Preferably, the process solution applying apparatus may further comprise a control device for controlling the supplying mechanism. The control device has an input section for receiving data representing the type of the resist solution and a supply speed control section for determining a rate of applying the process solution in accordance with the type of the process solution and for driving the supplying mechanism.
The rate of applying the process solution may have such a value that the solution applied in the prescribed amount forms a film having a uniform thickness on an entire surface of the substrate. In the case where the process solution is resist solution, it may be applied each time in an amount of 2.0 mL or less.
The solution may be heated to an appropriate temperature before it is applied to the substrate. The temperature depends upon the type of the solution. The solution may be one that contains a solvent or the like.
Preferably, the process solution applying apparatus may have a plurality of process solution supplying systems for supplying different types of process solutions. In this case, the apparatus further comprises a control device for controlling the supplying mechanism. The control device has a selection section for selecting one of the resist solution supplying systems in accordance with the type of the resist solution to be applied and a supply control section for determining a rate of applying the resist solution through the selected resist solution supplying system and for driving the supplying mechanism.
The supplying mechanism has a positive-displacement pump for drawing and discharging a prescribed amount of process solution and a stepping motor for driving the positive-displacement pump and changing a rate of discharging the process solution when controlled in terms of rotation speed.
The positive-displacement pump may be, for example, a bellows pump having bellows. The bellows may be driven by a ball screw mechanism which in turn is driven by the stepping motor.
According to another aspect of the present invention, there is provided a resist solution applying method comprising the steps of: holding a substrate; applying process solution in a prescribed amount to the wafer and at such a rate that the process solution forms a film having a uniform thickness on the substrate; and rotating the substrate holding mechanism, thus rotating the wafer at a predetermined speed to spread the process solution by virtue of centrifugal force and to coat the substrate with the process solution.
Those skilled in the art will understand the other features and advantages of the present invention will be understood from the following detailed description of the embodiments and by reference to the accompanying drawings.